[sr-dev] ideas on dialog spiral distinction

[Jason Penton]

Thanks guys, good points indeed - let me play around and see what I can come
up with.

The question is: if we find a clean solution would you be ok with adding it
into the repo? I suppose initially we could even implement with compile time
flag like "SPIRAL_UNIQUE_DLG" for example. Although, I don't particularly
like doing this sort of thing.

I think the question is: would everyone accept having to call
get_dlg(callid, ftag, ttag, branch) when according to RFC3261 a dialog
should be identifiable by only the 3 (cid, ftag, ttag).

IMO, this would be a good feature to add to Kamailio, so hopefully it can be
approved?

Cheers
Jason

On Thu, Aug 25, 2011 at 11:29 AM, Klaus Darilion <
klaus.mailinglists at pernau.at> wrote:

>
>
> Am 25.08.2011 11:16, schrieb Timo Reimann:
> > On 25.08.2011 10:31, Klaus Darilion wrote:
> >> > Am 25.08.2011 10:14, schrieb Jason Penton:
> >>> >>
> >>> >> From some initial work and testing I can confirm that this works
> ONLY
> >>> >> when using the top Via *without* branch tags. Not sure what impact
> this
> >>> >> could have?
> >>> >> This is because a BYE results in a different set of branch tags from
> the
> >>> >> original set of invite branches - I am investigating why and how
> this
> >>> >> works now.
> >> >
> >> > Sure. the branch tag is a transaction identifier and must be unique in
> >> > space and time. Thus, BYE must have another tag. That's why I said you
> >> > have to put some data into RR cookies - this is the only data which
> >> > stays the same during the dialog (except tags and call-id).
> >> >
> >> > If you only want to know if an in-dialog request is from orig->term or
> >> > from term->orig, then the is_direction function is already sufficient.
> >> >
> >> > If you want to detect a certain spiral leg in dialog module, IMO you
> >> > have to add another matching parameter (besides tags and call-id) to
> >> > dialog module which will be set as RR-cookie and retrieved from Route
> >> > header for in-dialog requests. Every time the initial requests spirals
> >> > through the proxy, you have to add such a cookie which of course must
> be
> >> > different to the previous inserted cookie (therefore ftag is not
> >> > sufficient anymore) - either generate a random identifier or reuse
> some
> >> > data from the message (e.g. you could copy branch-tag to RR header as
> it
> >> > should be unique)
> > Let me emphasize that you don't need to add a new RR cookie: You can
> > re-use the existing one that implements DID mode and simply extend the
> > hash function to cover that extra value you choose. (Random number or
> > branch parameter, as Klaus mentioned; see my comments below though.)
>
> Indeed - I have not thought about this parameter. If it would be
> extended to be unique it should work - as long as the DID value in
> in-dialog requests is correct. Thus, DID_FALLBACK mode would not work
> anymore.
>
> regards
> Klaus
>
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